The present invention relates to a bookbinding apparatus and an image forming system, particularly to a bookbinding apparatus for producing a booklet by binding a plurality of sheets of paper with adhesive, and an image forming system provided with such a bookbinding apparatus.
In the field of shortrun-printing, there has been widespread use of an image forming system for producing a booklet in one process from printing to bookbinding by combination between an image forming apparatus of high-speed image forming performance such as an electrophotographic image forming apparatus, and a bookbinding apparatus.
In contrast to the conventional bookbinding process wherein printing and bookbinding are performed in separate processes, such an image forming system has the advantage of modifying what is to be printed whenever required, despite its lower printing speed and bookbinding speed. This system is an image forming system characterized by high efficiency when evaluated in a comprehensive manner, and is utilized as a POD (Print On Demand) system.
In the POD system, the image forming apparatus is linked with the bookbinding apparatus. Further, the POD system is often installed in an office or a building shared by an office, not in a workshop particularly built for printing and bookbinding. This requires the POD system and its constituent parts to be designed in a compact configuration.
Thus, the bookbinding apparatus employed in this field produces a booklet by bundling sheets in a comparatively simple process of gluing.
The Unexamined Japanese Patent Application Publication No. 2000-168265 discloses a compact bookbinding apparatus wherein a bundle of sheets is moved to a coating roller to cause relative movement of the coating roller across the length of the spine of a bundle of sheets, whereby an adhesive is coated to produce a booklet. In the Patent Application Publication, a scraping roller is provided to control the thickness of the adhesive layer formed on the spine of a bundle of sheets. The space between the scraping roller and the spine of the bundle of sheets is adjusted according to the thickness of the bundle of sheets.
When a coating roller is used, adhesive is coated by the shuttle movement of the coating roller along the spine of the bundle of sheets. It has been revealed, however, that uniform coating cannot be ensured if one coating is provided in the forward or backward motion.
Such irregular coating causes insufficient adhesion in some portion, hence insufficient strength of the booklet, whereas an excessive amount of adhesive is found in other portions. This has been found out to reduce the quality of the booklet.
In many cases, booklets are formed by wrapping a bundle of sheets with a cover sheet.
FIG. 1 shows a booklet wherein the amount of adhesive is excessive. As shown in FIG. 1, a lump of uneven adhesive is formed on the boundary line between the sheet bundle SS and cover sheet S2, and the quality of the booklet is deteriorated by this lump. Further, projections and depressions are produced on the spine area of the cover sheet S2 to reduce the quality of the booklet.